The present invention relates to storage and process devices and more particularly, to a surge tank for degassed process material.
Polyurethane foam can be ground into fine particles using, for example, cryogenic processes or roll mills. These fine particles can then be used, for example, to replace chemicals in recipes for new polyurethane or new foam; this provides an environmental benefit and often a cost savings. “Polyurethane” (PUR) describes a general class of polymers prepared by polymerization of diisocyanate molecules and one or more active-hydrogen compounds. “Active-hydrogen compounds” include polyfunctional hydroxyl-containing (or “polyhydroxyl”) compounds such as diols, polyester polyols, and polyether polyols. Active-hydrogen compounds also include polyfunctional amino-group-containing compounds such as polyamines and diamines. An example of a polyether polyol useful in recipes for flexible polyurethane foam is a glycerin-initiated polymer of ethylene oxide or propylene oxide.
In order to add polyurethane powder to the recipe, the powder must be mixed with liquid reactants to form a slurry. Although the powder may be mixed with any of the liquid reactants—such as polyol, diisocyanate, water, surfactants, catalysts, and the like—it is generally preferred to mix the powder into the one or more liquid reactants that comprise the largest fraction of the mass of the recipe. This recipe component with the most mass is usually polyol. Polyols are described in considerable detail in “Polyurethane Handbook, 2nd ed.,” Gunter Oertel, Hanser/Gardner Publications, Inc., 1993, pages 55 to 72. Further, the slurry must be free of entrained bubbles because they create an undesirable irregular cell structure in the foam, including holes and splits. Powder can be mixed with liquid reactants in a batch process by adding a known mass of powder to a known mass of polyol, mixing thoroughly, and allowing sufficient time (generally about 8 to 48 hours) for entrained bubbles to leave the slurry. Such a natural de-gassing process takes a long time because the slurry has a high viscosity, generally about 500 to 20,000 mPa-s. The slurry viscosity increases with powder concentration, and concentrated slurries can have a viscosity in excess of 20,000 mPa-s. A continuous process for removal of entrained air is preferred over a batch process because the continuous process would not require waiting for entrained air to leave the slurry naturally, and the continuous processes would not require the large storage capacity necessary to hold the slurry needed for an entire day of foam production.
A need exists for devices and processing methods to take finely ground polyurethane-foam particles, disperse them as a slurry in polyol, remove substantially all entrained bubbles from the slurry, and to use this slurry as a direct replacement for at least some of the polyol in the production of new polyurethane articles. It is further desirable for such a process to be able to run continuously, such that powder and polyol are mixed, de-gassed, and used to make new polyurethane articles without delay. The desired continuous process must be able to deliver bubble-free slurry with accurately controlled solids concentration at an accurately controlled flow rate.